Thank you very much for your tips. With my irregual data I had to change my code( and data) and your tips helped alot.

In my check table (csv), I have 3 character codes(ICAO) and their equivalent 2 character codes(IATA) and descriptions. At first, IATA was at first column so I needed previous element of the array when the key was found. But after having an example of irregular ICAO code, which has 2 characters that matches its IATA code, the code didn't help since Perl stops after the first matching. And that IATA code is used three times in the table ( 1 ICAO, 2 IATA)

Then I changed IATA and ICAO columns' order and changed the code with your help and now it works. Though it may be clumsy, i think its pretty clear.

--$hash{'AirIATA'}= get_IATA($airlineLoc,$hash{'Airline'}) ;

-------------------------------------------------------

sub get_IATA
{
        my $file = shift;
        my $airline = shift;
        my @data;

        open(my $fh, '<', $file) or die "Can't read file '$file' [$!]\
+n";

        while (my $line = <$fh>)
        {
                my @fields = split(/;/, $line);
                push @data, @fields;
        }
        close($fh);

        my @results=    map
                {
                        $data[$_] =~ m{ \A \Q$airline\E }xms ? $data[$
+_ + 1] : ()
                }
                1 .. $#data;
        if ($#results>1)
        {
                return $results[1];
        }
        elsif ($#results>0) # Do I need a second check, like <2 ?
        {
                return $results[0];
        }
        else
        {
                print "Airline $airline has no definition in $file fil
+e\n";
                exit; # Program should stop if there is no match
        }
}
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